The present invention relates to power pumps; more specifically, the present invention relates to a spherical joint and bearing assembly between the connecting rod and the crosshead in a single acting, reciprocating power pump.
The power pumps to which this invention is directed are reciprocating pumps driven by power from an outside source like a diesel engine. The pump typically consists of a fluid end and a power end. The fluid end imports and pressurizes the fluid before it is expelled. The power end includes a crank shaft which transmits power and motion to a connecting rod which articulates the motion of the crank shaft to a crosshead. The crosshead, like a piston, creates a linear reciprocating motion derived from the crank shaft rotary motion through the connecting rod. The reciprocating motion of the crosshead is typically applied to a plunger and the plunger compresses fluid in the fluid end of the pump during the thrust portion of the pump cycle. To reduce wear, heat and friction, bearings are employed at each end of the connecting rod. For example, in current designs a cylindrical crank pin bearing is used between the crank shaft and the connecting rod to transmit the rotary load to the connecting rod. Similarly, a cylindrical wrist pin bearing is employed between the wrist pin and the connecting rod to transmit reciprocating load to the crosshead.
Bearing wear accounts for most down time and repairs of fluid reciprocating pumps. Specifically, the wrist pin bearing between the connecting rod and the wrist pin becomes worn and deformed from the load transmitted during the thrust stroke of the pump when the plunger and crosshead are acting against high pressure fluid being pumped through the fluid end of the pump. As the wrist pin bearing wears, it creates "slop" between the connecting rod and the crosshead causing the pump to knock as it operates. Increasing the bearing size and surface results in longer bearing life. However, the result is an unacceptable increase in pump size and weight.
An additional problem with prior art bearing arrangements is misalignment. Misalignment occurs when the crank shaft and the wrist pin or knuckle bearings are not perfectly parallel. Misalignment causes the bearings to wear on one side rather than evenly. This uneven wear results in a further reduction of bearing life.
There is therefore, a need for a bearing arrangement wherein the bearing surface is increased without increasing the diameter of the pump parts.
There is a further need therefore, for a bearing arrangement which will transmit force more evenly over the surface of the bearing, thus reducing bearing wear.
There is yet a further need for a bearing arrangement which is self-aligning and will reduce uneven bearing wear.